The stacking degree of freedom is a crucial factor in tuning material properties and has been extensively investigated in layered materials. The kagome superconductor CsV3Sb5 was recently discovered to exhibit a three-dimensional CDW phase below TCDW ~94 K. Despite the thorough investigation of in-plane modulation, the out-of-plane modulation has remained ambiguous. Here, our polarization- and temperature-dependent Raman measurements reveal the breaking of C6 rotational symmetry and the presence of three distinct domains oriented at approximately 120{\deg}to each other. The observations demonstrate that the CDW phase can be naturally explained as a 2c staggered order phase with adjacent layers exhibiting a relative π phase shift. Further, we discover a first-order structural phase transition at approximately 65 K and suggest that it is a stacking order-disorder phase transition due to stacking fault, supported by the thermal hysteresis behavior of a Cs-related phonon mode. Our findings highlight the significance of the stacking degree of freedom in CsV3Sb5 and offer structural insights to comprehend the entanglement between superconductivity and CDW.
@article{arxiv.2403.04391,
title = {$\pi$ Phase Interlayer Shift and Stacking Fault in the Kagome Superconductor CsV$_3$Sb$_5$},
author = {Feng Jin and Wei Ren and Mingshu Tan and Mingtai Xie and Bingru Lu and Zheng Zhang and Jianting Ji and Qingming Zhang},
journal= {arXiv preprint arXiv:2403.04391},
year = {2024}
}